Electric snap switch



April 5, 1949. A. M. MacFARLAND ELECTRIC SNAP SWITCH Original Filed July11, 1945 INVENTOR. fill A9022 %/Vac/Zrlczzzo/ Patented Apr. 5, 1949ELECTRIC SN AP SWITCH Allison M'. MacFarland, Naperville, 111., assignorto W. T. Neiman, Freeport, lll.

Original application July 11. 1945', Serial No. 604,382. Divided andthis application May 16, 1941, Serial No. 748,560

Ciaims. (01.200-67) This invention relates to improvements in electricsnap switches. More particularly, the invention pertains to snapswitches of the type wherein the snap action results from theapplication of forces applied by a leaf spring system having an unstabledead center position. This application is a division of co-pendingAllison M. MacFarland application now Patent No. 2,459,661, Jan. 18,1949.

The object of the invention is to provide a snap switch of improvedconstruction and operating characteristics. The device is extremelysimple and compact, and is adaptable for operation by a wide variety ofactuating impulses and over a broad range of capacities. The small spacerequired by the switch is a particular feature of this invention.

In the accompanying drawings,

Fig. 1 is a cross-sectional elevation of a complete snap switchembodying the invention;

Fig. 2 is a plan view of the leaf spring of the switch of Fig. 1;

Fig. 3 is a perspective view of the contact bar of the switch of Fig. 1;and

Fig. 4 is a diagrammatic view of the essential operating elements of theswitch.

Briefly, the switch consists essentially of a contact bar anchored atone end and having a free end which moves between stops, one or both ofwhich may be electrical contacts, and leaf spring actuating means. Theleaf spring comprises a tension leg or strip anchored at one end and acompression leg or strip rigidly connected at one end to an end of thetension strip in juxtaposition therewith. The free end of thecompression strip bears against a thrust seat on the contact bar in adirection calculated to place the contact bar in tension from the pointof anchorage. The switch is actuated by the application of a force whichshifts the position of the butt end of the leaf spring.

A simple embodiment of the invention is illustrated in Figs. 1 to 3 ofthe drawings. The switch mechanism is mounted upon a base 52 of ceramic,thermo-setting plastic, or other suitable structural insulating materialwhich, together with cover 52a forms a housing for the switch. Anelectrical contact 54 is fixed upon base 52 and is electricallyconnected to a suitable switch terminal by suitable means, asillustrated. A contact bar 56 is anchored at one end to base 52 by meansof an anchor pin or screw 51 supported in base 52 and electricallyconnected to a second switch terminal by suitable means, as illustrated.The free end 58 of contact bar 56 is provided with an electrical contactblock 59 which is adapted to engage contact 54 to close the switchcircuit.

Contact bar is actuated and its position controlled by the forces xertedby a leaf spring system. In the particular form of switch illustrated,this leaf spring 50 is a composite element formed by laying one strip ofsuitable spring metal upon another and firmly fastening the stripstogether at one end, as by riveting. The leaf spring is separatelyillustrated in Fig. 2. The upper strip 48 is anchored or fastened tofixed switch structure by suitable means such as insulating strip 53extending from electrical contact 54. It may be noted that the operationof the switch requires only that spring strip 48 be anchored to asupport, the fixed mounting being illustrated because of the greaterconvenience in assembly with this arrangement. The lower spring strip 49is stepped in thrust seat 55 provided to receive the end of the strip ata point near the free end of contact bar 55. This seat faces theanchored end of the contact bar and receives the thrust of compressionspring strip 49 outwardly from the anchorage at 51. The relative lengthsof spring strips 48 and 49 and the location of the anchorage of strip 48are such that strip 49 must be bowed in order to insert its end in seat55. In assembling the switch, strip 49 is depressed, and, being undercompressive stress in this position, the butt end of the leaf spring 50is urged upwardly against the switch actuating plunger 60.

In order to accommodate the bowed compression strip 49 of the spring andavoid the exertion of a sidewise force, the middle section of thecontact bar is depressed or an opening for the spring is provided. Whileany one of several forms of contact bar may be suitable, one which isbifurcated at the thrust seat to divide the middle section of thecontact bar into two space branches is illustrated in Fig. 3. The twobranches 6| are far enough apart to provide necessary clearance forspring strip 49 to move between them.

Unless the nature of the anchorage is such that movement of the contactbar between the fixed contacts or stop and contact is unimpeded thereby,the section of the contact bar adjacent the anchored end is madeflexible or hinged to permit this movement.

Operation of the device thus described may be explained by referencetothe diagrammatic illustration of the essential operating elements inFig. 4. In this diagram, the character T designates the spring stripwhich is under tension in 3 the spring system and the characterdesignates the strip which is under compression. The correspondingelements of the switch of Fi 1 are strips 48 and 40, respectively. Thecharacter P designates the arrow which represents the downward forceapplied by means of plunger 0. other elements of the diagram are readilyrelated to the mechanical counterparts in the switch structure of Fig. 1by the similarity of numeral designation.

The switch mechanism trated in Fig. 4 is one in cult is normally open.'The face contact end 58' of contact bar 56' restsupona stop formed by aportion of insulating base 52'. with the spring system anchored at 53'and the free or butt and of the spring ill maintained at a given levelby the force P, a thrust or force having both horizontal and verticalcomponents is exerted at seat 55' of the contact bar it. The portion ofthe contact bar between step or seat 55' and the anchorage 51' is undertension, this condition being maintained'for all positions of thiselement.

Analysis or the efl'ective forces of the spring system shows that thevertical component of force applied by the spring to the contact bar atseat 5-5 may be altered in magnitude and reversed in direction by.varying the magnitude of force P and thus the position of the butt endof the spring. As this force is increased, the butt end of the leafspring is depressed, the magnitude of the stresses in tension strip Tand compression strip C are increased and the direction of the resultantforce applied to the contact bar at seat 55' changes. Although it istheoretically possible to apply a force at P which will result in ahorizontal resultant force at seat 55 without vertical components, thisbeing the condition for placing the switch mechanism in dead centerposition, the system is extremely unstable under such conditions and thedead center status is impossible to attain in practice. Actually, as theforce P is increased, the downward component of force or contact end ofcontact bar 56' against the insulating stop 52 abruptly changes to anupward component which starts the contact end 58' of the bar in upwardmotion. This initial displacement moves the point of application of theforce of the spring system at seat 55' upwardly with the result that theupward component of force is increased and the motion of the bar greatlyaccelerated. The result is a snap action in bringing the contact end 58'of bar 56' into engagement with contact SI. Similarly, diminution of theforce P permits the free end of the leaf spring to move upwardly,opening the switch with a snap action.

Special attention is directed to the nature and effect of a lateral aswell as a longitudinal force exerted by the compression strip 0 of thespring system. This leg of the leaf spring, being bowed and depressedbelow the general level of the tension strip T, exerts an upward forceupon the contact bar due to the deformation of this spring strip at thepoint of junction with the butt end of the spring 50. Thus, thecompression strip becomes afloating cantilever. This force, which isonly one element of the resultant force applied to the thrust seat, hasthe effect of lowering the dead center position of the contact bar andserves to accentuate the snap action. The latter effect is the result ofan increased deformation of compression strip C as the butt end of thediagrammatically illus-' which the internal cir-- which holds the free 4spring is depressed, the end of the strip in the thrust seat being belowthe center of rotation of the opposite. end of the strip and thusapproached as the butt end of the spring is depressed The extent oftravel of plunger- I and the magnitude of the force which must beapplied ployed.

to this plunger in order to operate the switch depend, in part, upon thelocation of the point of application of this force. In Fig. 1 theplunger engages the leaf spring near the free end. This force may beapplied either at the butt end of 'the'spring or it may be applied atany point along the length of the tension strip 48. Down-' ward pressureapplied, for example, midway between the anchorage on support member 53and the junction of the tension strip with the compression strip has theeffect of lowering the entire spring assembly at the same time as thefree end is depressed. A greater force is required with lessdisplacement at the lowering of the entire spring assembly under theinfluence of the depressing force appears to improve the snap action.

On the other hand, a switch to be operated with a smaller force andgreater plunger travel may be provided by extending the tree end of thespring in the manner suggested by the diagrammatic illustration of Fig.4. When the spring is so extended, the flexible extension absorbs aportionof the motion of plunger 60, the result being a differentactuating characteristic.

It will be appreciated that the form of the several elements of theswitch herein described may be altered without departing from the modeof operation of the essential mechanism. Particularly, various forms ofcontact bar may be em- Also, the structure may be readily adapted toduplex and multiple switch embodiments. Additional spring elements maybe emv ployed for this purpose.

The invention is claimed as follows:

1. A snap switch comprising a switch base, a

pair of fixed stops at least one of which is an electrical contactmounted in said base, an electrically conductive contact bar anchored atone end to said base and having a tree end movable between said stopsand a thrust seat arranged near said free end and facing the anchoredend thereof, and spring means for actuating said contact bar, saidspring means comprising a composite leaf spring comprising twosuperposed spring strips rigidly fastened together at one end, the freeend of the upper strip being anchored in fixed relation to said base,the lower strip being bowed in compression and its free end stepped inthe thrust seat upon said contact bar, and means responsive to externalmanipulation for depressing said composite leaf spring to actuate theswitch. 2. A snap switch in accordance with claim 1 in which the fixedstops are so arranged that upward movement of the free end of thecontact bar is limited to a point at which the thrust seat is below thelevel of the anchored end of the upper spring strip.

3. A snap switch in accordance with claim 1 wherein said lower springstrip is bowed sumciently to bring a portion of the strip below a lineextending from the thrust seat to the point of anchorage of the contactbar and said contact bar is bifurcated at the thrust seat to form anopening in the middle section of said bar to accommodate said lowerstrip.

4. A sna switch in accordance with claim 1 wherein at least the portionof said contact bar adjacent the anchored end thereof is flexible in thedirection of movement of said bar.

5. A snap switch comprising a switch base, a pair of fixed stops atleast one of which is an electrical contact mounted in said base, anelectrically conductive contact bar anchored at one end to said base andhaving a free and movable between said stops and a thrust seat arrangeda depressing said composite leaf spring to actuate the switch.

ALLISON M. MAOFARLAND.

REFERENCES CITED near said free end and facing the anchored end- 10 IThe f win r ferences are of record in the thereof, and spring means foractuating said contact bar, said spring means comprising a compositeleaf spring composed of two superposed spring strips rigidly fastenedtogether at one end.

file of this patent:

UNITED- STATES PATENTS Number Name Date the free end of the upper stripbeing anchored u 2.170.748 Eaten 22, 1939 Patent No. 2,466,459.

April 5, 1949.

that error appears in the printed specification of the above numberedpatent requiring correction as follows:

Column 3, line 13, for the Word face" readfree;

JOE E. DANIELS,

Assistant Commissioner of Patents.

